The invention is directed to new bisguanamines and their use in the stabilization of formaldehyde solutions.
There are already known phenylene bisguanamines of the formula ##STR2## (see German AS No. 2,358,856). Besides there are known alkylene bisguanamines of the formula ##STR3## in which n is a number from 1 to 8, see Booth, Chemistry and Industry Aug. 3, 1968, page 1047. The entire disclosure of Booth is hereby incorporated by reference and relied upon.
Aqueous formaldehyde solutions, especially solutions having a formaldehyde content above 30 weight percent are unstable if the temperatures at which they are stored fall below a certain minimum. There occurs turbidity through the formation of formaldehyde oligomers and finally the precipitation of paraformaldehyde. The higher the concentration of formaldehyde and the lower the storage temperature the more unstable are the solutions. Accordingly to the data in the monograph, "Formaldehyde" by J. F. Walker, 3rd edition, page 95, a 30 percent formaldehyde solution remains stable for up to about 3 months if it is held at at least 7.degree. C. For a 37 percent solution the required minimum temperature is 35.degree. C., for a 45% solution 55.degree. C. and for a 50% solution 65.degree. C. However, a disadvantage of the use of higher storage temperatures is that formic acid forms to a considerable extent in the formaldehyde solutions. This causes corrosion and is particularly disturbing in the use of formaldehyde solutions for condensation reactions.
The above mentioned values refer to formaldehyde solutions which contain less than 1 weight percent methanol as a stabilizer. To be sure by using higher methanol concentrations there can be produced equal storability at lower temperature, but there are required disproportionately high methanol concentrations. For example there is needed in a 37 percent formaldehyde solution for a storage temperature of 21.degree. C., a methanol content of 7%, for 7.degree. C. a methanol content of 10% and for 6.degree. C. a methanol content of 12%. The addition of methanol, however considerably increases the cost of the formaldehyde solutions, especially since the methanol is generally lost in using the solutions. Apart therefrom through the methanol the speed of reaction in numerous condensation reactions, for example in the condensation with malamine, is reduced.
Besides methanol there are known as stabilizers (for formaldehyde), ethanol, propanol-1, propanol-2, ethylene glycol, glycerine, urea, methyl urea, dimethyl urea, thiourea, diethyl thiourea, formamide, melamine, methylol melamine and acetoxime (J. F. Walker, "Formaldehyde", third edition, page 95, U.S. Pat. No. 2,000,152, U.S. Pat. No. 2,002,243 and Swain U.S. Pat. No. 2,237,092). However, these materials must be used in concentrations of at least 2% to be effective.
Stabilizing agents which can be used in lower concentrations are for example ether, acetals of polyhydric alcohols such as pentaerythritol, sorbitol and polyethylene glycol, esters of these polyhydric alcohols and higher fatty acids, higher alcohols such as heptanol, octanol, decanol, hydroquinone, polyvinyl alcohol, its esters and acetals (Halpern U.S. Pat. No. 3,183,271; British Pat. No. 1,129,507 and Japanese patent 30-3396. However, a disadvantage is that the activity of these materials is insufficient at lower concentrations and temperatures.
Furthermore, it is known to add as stabilizers lipophilic colloids such as polyoxyethylene lauryl ether (HLB (hydrophilic, lipophilic balance)-value=9.5), lipophilic sorbitol esters of higher fatty acids such as sorbitol monolaurate (HLB value=8.6) or soluble or partially soluble hydrophilic colloids such as methyl cellulose, hydroxypropyl methyl cellulose, ethyl cellulose, gelatin, pectin and cellulose acetostearate. They are used in concentrations below 0.1% or below 0.5% (German OS No. 1443566, Prinz U.S. Pat. No. 3,137,736). Also in these cases the stabilizing action in formaldehyde solutions having a methanol content below 1% at low temperatures is not sufficient.
There also have been used as stabilizers 2,4-diaminotriazine (1,3,5) or its methylol derivatives which contain in the 6-position an aliphatic residue having 7 to 9 carbon atoms or an alkoxy or an alkylmercapto group having 5 to 10 carbon atoms (Bornmann German Pat. No. 1205073 and Belgian Pat. No. 719245). Bornmann shows that alkyl guanamines having an alkyl chain length of below 7 carbon atoms or above 9 carbon atoms are poorer stabilizers than those with 7 to 9 carbon atoms. The stabilizer effect goes down even further as the alkyl group increases from 11 to 15 carbon atoms. For a good stabilizing effect the concentration of the added aminotriazine must be 0.05 to 0.2%.
There have also been employed for stabilizing formaldehyde solutions, mixtures of guanamines, for example butyroguanamine, benzoguanamine, acetoguanamine and their methylol derivatives with fatty acid esters, ethers or acetals of a polyhydric alcohol, hydroquinone, polyvinyl alcohol as well as esters or acetals of polyvinyl alcohol. In these mixtures the guanamine must be used in concentrations of 0.08%, especially of 0.1% if a sufficient activity is to be attained (Matsuora, German AS No. 1219464).
Besides it is known to use as stabilizers methoxymethyl, ethoxymethyl, propoxymethyl and butoxymethyl derivatives of aceto-, propio-, butyro- and benzoguanamines which are mixed with reaction products of formaldehyde with ethylene glycol, propylene glycol, polyethylene glycol, polypropylene glycol, glycerine, trimethylolpropane, pentaerythritol, sorbitol or polyvinyl alcohol and with aceto-, propio-, butryo- or benzoguanamine or with methyl-, ethyl-, propyl-, butyl-, cyclohexyl-, benzyl- or phenyl melamine (Ishizuka German AS 1268608). The concentrations in which the various guanamines or their mixtures are employed lie between 0.0025 and 0.06%. However, at these low stabilizers concentrations an elevated storage temperature is required if there is to be produced a sufficient stability of the formaldehyde solutions. If higher concentrations, namely 0.001 to 0.1% of the guanamine are used with 0.1 to 1.0% of melamine (Dakli German Pat. No. 1768915) it is true that the stabilization is better but the reactibility of the formaldehyde for condensation is reduced considerably.
It is also known that the activity of the guanamines or their methylol derivatives can be increased if there are additionally used hydrophilic polyglycol ethers of fatty alcohols or of partial esters of polyhydric alcohols with fatty acids or ion-active surface active substances such as phosphoric acid esters of nonylphenyl polyethylene glycols. However, also in these cases the activity is still not satisfactory.
Finally there is also known the employing of phenylene bisguanamine as stabilizer (Diem, German AS 2358856). This material it is true shows a better activity, however, it is relatively difficultly accessible and particularly exhibits the disadvantage that it is very difficultly soluble. Therefore it is difficult and requires much time to bring the necessary amount of stabilizer into soluble form. The alkylene bisguanamines (II) are to be sure considerably easier to dissolve, but they have either no stabilizing effect or only very small stabilizing effect.